Medicare will pay for specialized brain scans in patients with atypical symptoms of Alzheimer’s disease, according to the Centers for Medicare & Medicaid Services.

The makers of the technology, known as positron emission tomography, or PET, struggled for four years to gain reimbursement approval from CMS. However, because PETs cannot tell by themselves whether or not a person has Alzheimer’s disease, the agency said patients only qualify if they exhibit irregular symptoms of the disease and if doctors believe they may instead have one of several rare brain diseases known as “fronto-temporal dementia.”

These conditions most often occur at a younger age than typical Alzheimer’s symptoms and become apparent through behavioral changes and language difficulties rather than memory loss. The conditions can mimic Alzheimer’s enough that the PET scan is necessary to help determine which disease the patient has. These dementias generally progress more rapidly than Alzheimer’s, according to a CMS report.

The scans cost about $2,000 and involve injecting radioactive chemicals. CMS approved the limited use of PET scans because they tend to provide more substantial evidence of the diseases than a doctor’s prognosis based on symptoms alone, according to an agency memo.